Assessing the effectiveness of two supplementation programs for Atlantic salmon recovery in Nova Scotia

Abstract

Atlantic salmon populations have experienced severe declines across their range, prompting the use of hatchery-based supplementation strategies to support recovery efforts. To inform conservation practices, this thesis evaluates the post-release performance of two supplementation strategies used in Nova Scotia: traditional hatchery smolt releases and smolt-to-adult supplementation (SAS). Using acoustic telemetry, Chapter 1 compared hatchery-reared and wild smolts in the LaHave River with acoustic telemetry, revealing lower survival among hatchery smolts driven largely by predation in lake habitats during outmigration. Hatchery smolts had slower migration speeds in upstream reaches compared to wild smolts, but comparable river exit timing and early marine migration routes. Chapter 2 assessed the survival, behaviour, and migration patterns of SAS and wild adult salmon in Cape Breton rivers using acoustic telemetry. SAS adults exhibited significantly lower freshwater survival, higher acceleration levels, atypical river movements, premature river exit, and altered marine migration routes, with captivity duration influencing both survival and potential spawning behaviour. Collectively, these findings demonstrate that captivity imposes behavioural and likely physiological changes that reduce fitness in the wild, with different post-release challenges arising across life stages and supplementation programs. Effective supplementation will require life-stage-specific strategies, including optimizing smolt releases below known predation hot-spots, reducing captivity duration for SAS adults, and modifying SAS release practices (such as gradually decreasing feeding pre-release to replicate the fasting state of wild returning adult salmon and staggering releases across known spawning grounds). Without improvements to post-release performance, supplementation programs may likely fail to achieve their intended conservation goals.